A teen girl and her infant sister were found dead and their mother was found unresponsive at a home in Ontario Tuesday, officials said.

The girls’ father called 911 around 4 p.m. to report unknown trouble at the residence on the 500 block of East Tam O’Shanter Street, said Ontario Police Sgt. Bill Russell.

The deaths of the 14-year-old and 4-month-old were being investigated as suspicious, police said.

The unresponsive mother was hospitalized with “slight injuries” and later listed in stable condition, Russell said. The sergeant did not describe the nature of the woman’s injuries and said he wasn’t sure how they were sustained.

“Because she was unresponsive, I don’t know if that was an internal thing or something that was done externally,” he said.

Police wouldn’t say if there was any sign of a struggle, but Russell did say there weren’t any noticeable noxious fumes in the air.

“This is highly unusual,” the sergeant said. “I’ve been on the job for 20 years. This is not a call you get very often.”

Coroner’s officials were at the scene Tuesday evening working to determine the children’s cause of death.

Police noted that there was no further threat to the neighborhood.

The father was taken to the police station for questioning but had not been placed under arrest, according to Russell.

Detectives were working to determine whether he was home when the deaths occurred or whether he came back to find his family members not breathing, Russell said.

“Right now, until we have an idea of if this was accidental or there was an intentional act, we can’t determine if anybody’s a suspect,” he said.

A man at the scene who identified himself as a cousin of the family’s said he was shocked by the news.